WBR0977
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| Author | [[PageAuthor::Rim Halaby, M.D. [1] (Reviewed by Yazan Daaboul, M.D.)]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Biochemistry |
| Sub Category | SubCategory::General Principles |
| Prompt | [[Prompt::A scientist studies the expression and enzymatic activities of aldose reductase and sorbitol dehydrogenase using western blotting and immunohistochemistry techniques. The study is conducted on samples of human cells obtained from multiple organs. In one sample, the expression of only aldose reductase is positive, whereas the expression of sorbitol dehydrogenase is completely absent. The sample is most likely obtained from which of the following organs/tissues?]] |
| Answer A | AnswerA::Liver |
| Answer A Explanation | [[AnswerAExp::Sorbitol dehydrogenase is present in the liver.]] |
| Answer B | AnswerB::Retina |
| Answer B Explanation | [[AnswerBExp::Sorbitol dehydrogenase is absent in the retina. The obtained sample of cells lacking sorbitol dehydrogenase in the study is likely derived from the retina.]] |
| Answer C | AnswerC::Ovaries |
| Answer C Explanation | [[AnswerCExp::Sorbitol dehydrogenase is present in the ovaries.]] |
| Answer D | AnswerD::Seminal vesicles |
| Answer D Explanation | [[AnswerDExp::Sorbitol dehydrogenase is present in the seminal vesicles.]] |
| Answer E | AnswerE::Lens |
| Answer E Explanation | [[AnswerEExp::Sorbitol dehydrogenase is present in the lens albeit in low concentrations.]] |
| Right Answer | RightAnswer::B |
| Explanation | [[Explanation::The sorbitol pathway involves 2 major reactions that result in production of fructose. Glucose is converted to sorbitol by the action of aldose reductase; then sorbitol is converted to fructose by the action of sorbitol dehydrogenase. Sorbitol dehydrogenase is present in the seminal vesicles, ovaries, liver, and the lens. In contrast, it is absent in the retina, Schwann cells, and the kidneys. Therefore, when glucose concentration is chronically elevated (e.g. individuals with long-standing uncontrolled diabetes mellitus), glucose is continuously converted to fructose. In organs that lack sorbitol dehydrogenase, accumulation of sorbitol results in osmotic damage and target organ complications (cataract, retinopathy, and neuropathy among diabetic individuals). Shown below is a figure that illustrates sorbitol metabolism |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Sorbitol, WBRKeyword::Sorbitol dehydrogenase, WBRKeyword::Lens, WBRKeyword::Retina, WBRKeyword::Liver, WBRKeyword::Ovaries, WBRKeyword::Seminal vesicles, WBRKeyword::Retina, WBRKeyword::Kidneys, WBRKeyword::Aldose reductase, WBRKeyword::Osmotic damage, WBRKeyword::Diabetes mellitus, WBRKeyword::Glucose, WBRKeyword::Sorbitol pathway |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |
